The present disclosure relates to additive manufacturing systems for printing three-dimensional (3D) parts and support structures. In particular, the present disclosure relates to printing sacrificial support structures to support a part built in a layerwise additive process.
Additive manufacturing is generally a process in which a three-dimensional (3D) object is manufactured based on a computer image of the object. The basic operation of an additive manufacturing system consists of slicing a three-dimensional computer image into thin cross sections, translating the result into two-dimensional position data, and feeding the data to control equipment which manufacture a three-dimensional structure in a layer wise manner using one or more additive manufacturing techniques. Additive manufacturing entails many different approaches to the method of fabrication, including fused deposition modeling, ink jetting, selective laser sintering, powder/binder jetting, electron-beam melting, electrophotographic imaging, and stereolithographic processes.
In a jetting or drop-on-demand process, a building material is jetted in droplets from a dispensing head having a set of nozzles to deposit layers on a supporting structure. Depending on the fabrication technique and material type, the layers may then be planarized, cured and/or solidified using a suitable device. The building material may include part material, which forms the object, and support material, which supports the object as it is being built.
In an electrophotographic 3D printing process, each slice of the digital representation of the 3D part and its support structure is printed or developed using an electrophotographic engine. The electrophotographic engine generally operates in accordance with 2D electrophotographic printing processes, using charged powder materials that are formulated for use in building a 3D part (e.g., a polymeric toner material). The electrophotographic engine typically uses a support drum that is coated with a photoconductive material layer, where latent electrostatic images are formed by electrostatic charging following image-wise exposure of the photoconductive layer by an optical source. (Alternatively, an image may be formed using ionography by direct-writing electrons or ions onto a dialectric, and eliminating the photoconductor, all within the scope of the present invention and within the use of the electrophotography terminology as used herein). The latent electrostatic images are then moved to a developing station where the polymeric toner is applied to charged areas, or alternatively to discharged areas of the photoconductive insulator to form the layer of the charged powder material representing a slice of the 3D part. The developed layer is transferred to a transfer medium, from which the layer is transfused to previously printed layers with heat and/or pressure to build the 3D part.
In fabricating 3D parts by depositing layers of a part material, supporting layers or structures are typically built underneath overhanging portions and in cavities of objects under construction, which are not supported by the part material itself, and may also be built around sidewalls of the part. An additional geometry acting as a support structure is generated in software, and typically is sliced with the part to prepare a digital image for printing. A support structure may be built utilizing the same deposition techniques by which the part material is deposited. The support material adheres to the part material during fabrication, and is removable from the completed 3D part when the printing process is complete. In some 3D printing processes, such as an electrophotographic 3D printing process, involving utilizing pressure and temperature when transfusing each layer, the support structures also provide back pressure for a transfer medium during transfusion of imaged layers as a part is built. After a part is built, the support structure is removed from the part, for example by being dissolved or disintegrated in an aqueous solution or dispersion. Removal of the support material can be a time consuming process, significantly increasing the time to make a 3D part available for use. Further, the support material itself, as well as the removal of the support material, adds significant cost to the process of printing a 3D part.